4 C. E. VAN HISE THE PROBLEM OF THE PRE-CAMBRIAN 



"an ancient Keewatin lava has, in places, been subjected to a little denuda- 

 tion before the deposition of the Grenville limestone, which fills the cracks and 

 openings in the ropy surface of the lava. Unconformably above the Grenville 

 limestones and Keewatin lavas or greenstones rest the conglomerates and 

 other sedimentary rocks, including limestones, which the present writers class 

 as Huronian." 



Thus, according to Miller and Knight, there is in the Hastings area a 

 series of rocks bearing limestone which is the equivalent of the Gren- 

 ville; but to the upper series of rocks, which were not given a definite 

 place by the International Committee, thej^ would apply the term 

 Hastings and place this series in the Huronian. 



Miller and Knight do not expressly indicate whether the unconformity 

 Avhich they recognize is at the same horizon as that discovered by the 

 International Committee, but presumably this is the fact. If this be so, 

 their Avork determines the point left unsettled by that committee as to 

 the importance of this unconformity and shows that it has great struc- 

 tural significance. The discovery that the upper series contains a lime- 

 stone formation as well as the Grenville series is of great importance, 

 for it means that it yet remains to discriminate separately upon the geo- 

 logical map the area! extent of the two series containing the different 

 limestone formations of the Hastings district. 



Until these two series are separately mapped and the limestone is dis- 

 tributed between them, I am unwilling to commit myself as to the prob- 

 able position of the Grenville series. If, as Miller's work intimates, the 

 Grenville has been laid down iipon an ancient eroded Keewatin floor, it 

 may be equivalent to the lowest of the Huronian series, to be later dis- 

 cussed. Whatever the position of the Grenville proper, the upper series 

 of the Hastings district, which may be called the Hastings series, in all 

 probability is of Huronian age, probably Middle Huronian or Lower 

 Huronian. 



The origixal HuROjsriAN District 



After having been several years in Canada, Sir William Logan began 

 systematic work upon the north shore of lake Huron, with Alexander 

 ]\Iurray as his assistant. In this Lake Huron work the name of Murray 

 should always be associated with that of Logan. The former furnished 

 the broad ideas ; the latter carried them out with great patience in an ex- 

 tremely rough countr}', covered with a dense forest, of which there was 

 no map other than the land surveys. No one who has not attempted to 

 work out intricate geology in the tangled forest of an unbroken wilder- 

 ness without adequate maps, and been tortured by the innumerable insects 



